Im assuming it isn’t because bleach is just a really good white paint.
In: Chemistry
[Bleach](https://en.wikipedia.org/wiki/Sodium_hypochlorite) is an oxidizer; it contains oxygen and chlorine ions that react aggressively with organic compounds and even metals. So basically what happens is the pigments that are used to add color to clothes get oxidized (with the oxygen or with the chlorine) and either lose their color as a result, or detach from the cloth fibers.
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